This invention relates to computers protected against loss of primary electric power and, more particularly, to a rapid controlled power-down while freezing an application program stage and work product for resumption at a future time.
Computers are utilized in numerous locations, including the home and industry, and are powered by electricity which is obtained, normally, from electric power lines provided by an electric power company. There are times, such as during an electrical storm, by way of example, when electric power may be interrupted unexpectedly. The interruption of power may occur while a human operator is entering data as by a keyboard, to the computer as in a word processing program. Or, by way of further example, the interruption in power may occur while the computer is performing a lengthy mathematical procedure, such as the inversion of a matrix, or the calculation of pixel data in the display of a rotated view of complex machinery or other subject matter in a program for computer-aided design. It is important to provide the computer with some sort of backup power so as to save the computer operator from the inconvenience of lost data and the possible need to redo a lengthy project.
One solution to the problem brought on by an interruption of electric power is to employ a bank of large batteries, such as automotive batteries, which have sufficient stored energy to operate the computer for many hours, so as to allow the operator to complete his or her work on the computer. The batteries are connected through suitable power circuitry which enables battery power to be applied to the computer instantaneously upon the loss of the primary power so as to insure the absence of any transient response in the computer during a switching from primary power to backup power. While such an arrangement of large batteries can insure proper operation of the computer during a power interruption, the presence of the bank of batteries would present, in many situations, an undesirable burden both in terms of space requirements and in terms of the necessity for maintaining the batteries in a proper state of electrical charge.
It is recognized that, in most situations, it is not necessary to provide a long term supply of back-up power because many power interruptions persist for less than a minute, or possibly for several minutes. A power outage lasting for one or more days is rare.
Therefore, the major concern in protecting a computer from a power interruption is the need to preserve data which has been generated during the running of an application program, and to reserve the stage of operation of the program, as in the foregoing examples of the inversion of a matrix or the rotation of a view, so that the operator of the computer can resume use of the computer at a convenient time subsequent to the resumption of the electric power. It is also recognized that, by use of a power-down procedure employing no more than a minimal amount of time, the amount of energy which must be stored for backup power is minimized, thereby avoiding the use of excessively heavy and bulky batteries. Indeed, if the power-down procedure could be accomplished within a matter of seconds, then the back-up power could be provided by relatively small rechargeable batteries which could be mounted conveniently within the computer itself. With such a construction, the computer could be manufactured with its own protection against power interruption, and would provide the operator with the facility for resuming the computer operation at the same point where the computer operation stopped at the onset of the power outage.
Presently available equipment for protection of computers from power interruptions does not provide the foregoing type of protection. By way of example, external batteries are required to provide an adequate reserve of electric energy for use during a power-down procedure. Also, external storage apparatus for storing data from the computer is employed during a power outage. Also, proposed power-down systems contemplate the closing of application programs in use by the computer prior to shutting down the computer. This can entail a significant amount of time in the situation where a person may be operating simultaneously with a word-processing program, a spread-sheet program, a graphics program, and a mathematical program. Furthermore, upon the resumption of computer activity after restoration of the power, it would be necessary for the operator to reopen all of these programs, and to reestablish the various stages in the operations of these programs to resume the work procedure at the point at which the work was previously terminated. This presents a considerable inconvenience to the operator.